1. Field of the Invention
The present invention relates to a vibration isolating apparatus for reducing vibrations from a vibration source.
2. Description of the Prior Art
A vibration isolating apparatus, generally known as a rubber vibration isolator, is employed for mounting, for example, the engine of an automobile so as to absorb the vibrations of the engine such that no vibration is transmitted to the vehicle body.
One type of previously proposed vibration isolating apparatus has such a structure that a fluid is sealed in a hollow chamber of a vibration absorbing main body which is mainly constituted by a hollow molded article of a resilient material, and a tubular portion is connected to the hollow chamber. The vibration isolating apparatus is arranged such that the vibration acting on the hollow chamber causes what is called air-column resonance in the tubular portion whereby it is possible to damp the vibration by a large margin.
The above-described conventional vibration isolating apparatus, however, suffers the following problem. Since the mass of the fluid in the tubular portion has an effect on the resonance frequency, it is necessary to increase the length of the tubular portion to an extreme extent in order to obtain a desired vibration damping characteristic. In particular, when air is employed as the vibration absorbing fluid, since its resistance against the tubular portion is large, the friction occurring between the tubular portion and the vibration absorbing fluid is correspondingly large, which fact disadvantageously involves an adverse effect on the occurrence of the resonance.